1. Field of the Invention
The invention is in the field of manufacturing a plurality of optical elements, for example refractive optical elements or diffractive micro-optical elements, on a waver scale by means of a replication process that includes embossing or moulding steps. More concretely, it deals with a method of replicating an optical element.
2. Description of Related Art
Replicated optical elements include transparent diffractive and/or refractive optical elements for influencing an optical beam in any pre-defined manner, refractive elements such as lenses, potentially at least partially reflecting elements etc.
When optical elements are produced by replication, there is often a basic configuration involving a substrate and a replication tool, and replication material being placed in contact with the substrate and/or the replication tool. The replication tool comprises a replication structure being the negative of a surface structure of the element(s) to be replicated. In the course of a replication process, the replication material is hardened, and thereafter the replication tool is removed, the replication material remaining in contact with the substrate.
Of special interest are the wafer-scale fabrication processes, where an array of optical elements is fabricated on a large-scale, for example disk-like (“wafer-”) structure, which subsequent to replication is separated (“diced”) into the individual elements or stacked on other wafer-like elements and after stacking separated into the individual elements, as for example described in WO 2005/083 789. ‘Wafer scale’ refers to the size of disk like or plate like substrates of sizes comparable to semiconductor wafers, such as disks having diameters between 2 in and 12 in.
In the following text, the substrate is sometimes referred to as “wafer”. This is not to be interpreted as being limiting in terms of size or shape of the substrate, rather, the term denotes any substrate suitable for an array of optical elements that are, at some stage subsequent to the replication process, diced into a plurality of components.
Often, optical elements manufactured by replication process include replicated structures on both sides of a wafer, the two sides together, for example, constituting a lens singlet. In such a process, the structures on the second side must be aligned with the replicated structures on the first side. This is typically done in a so-called mask aligner where the tool is aligned to some structure on the wafer. With the tool held in place by some mechanical features, the replication material is then hardened, for example by being exposed to some activation energy, for example in the form of UV radiation. Since the hardening process is usually comparably time consuming, for mass production a large number of mask aligners would have to be used, so that several replication processes can be carried out in parallel. Also, as for the alignment step, mask aligners have to be operated manually, a lot of personnel or a lot of coordination is required.